This invention relates generally to semiconductor technology and more particularly to the method of forming thin film transistors (TFTs) on polycrystalline silicon regions within an amorphous silicon film.
Polycrystalline silicon is formed by crystallizing amorphous silicon films. One method of crystallizing amorphous silicon films is excimer laser annealing (ELA). Conventional ELA processes form polycrystalline films having a random polycrystalline structure. Random, as used here, means that no single crystal orientation is dominant and that polycrystalline structures consist of a mixture of crystallographic orientations in silicon. These crystallographic orientations in silicon are commonly denoted as <111>, <110>, and <100>, along with their respective corollaries, as is well known in the art. Control of crystallographic orientation is generally desirable because the electrical characteristics of a polycrystalline silicon film depend upon the crystallographic orientation of the film. In addition, the uniformity of the electrical characteristics will improve if the majority of the film has a controllable texture.
ELA, as well as many other annealing methods, has not provided a means to control these microstructural characteristics and achieve a predictable and repeatable preferential crystal orientation and film texture within an annealed film. It would be desirable to have a method of producing TFTs using a polycrystalline silicon film with a more uniform crystallographic orientation. It would also be desirable to be able to produce TFTs using predominantly <100> polycrystalline silicon.